Export the below file to ODT.  You will see the following stacktrace.

Debugger entered--Lisp error: (error "Stack overflow in equal")
  gethash(((table (:type org :attr_odt (":style \"GriddedTable\"") :parent)) . 0))
  org-export-table-cell-width((table-cell (:parent (table-row (:type standard )))) )
  org-odt-table-cell((table-cell ))
  org-export-data((table-cell ))

Just to remind you, the table is created on fly by manipulating the
tree.  Using an `eq' as predicate in `org-export-table-cell-width'
solves the problem.  I am not sure this would be the right fix though. 

The last I have seen/worked (which is long time back), there was no
caching.

ps: If you aren't seeing the above trace in org repo, just pull from my
repo.

Web URL: http://repo.or.cz/w/org-mode/org-kjn.git
Pull URL: http://repo.or.cz/r/org-mode/org-kjn.git